[citation needed] Rheumatoid arthritis is an autoimmune disease that is characterized by inflammation of the synovial joints due to attack by the body's own immune system.

In this condition, the white blood cells travel through the bloodstream to the synovial joints and release pro-inflammatory cytokines upon arrival.

The pannus receives blood supply from the newly formed vessels and grows inward, invading the articular cartilage and bone within the joint.

Due to the increased inflammatory response of the body's immune system, this condition can cause a reduction in red and white blood cells.

When the spleen becomes enlarged, it is a strong sign of infection somewhere in the body and can be caused by inflammatory conditions such as rheumatoid arthritis.

The increased need for production assistance of white blood cells to affected areas causes hyperfunction of the spleen.

[10] The spleen is found in the left upper quadrant (LUQ) of the peritoneal cavity and due to its enlargement, can cause stress on neighboring organs.

[11] The presence of three conditions: rheumatoid arthritis, an enlarged spleen (splenomegaly), and an abnormally low white blood cell count are indications that Felty's syndrome is possibly occurring.

It is commonly overlooked or misdiagnosed as other conditions (e.g., leukemia, systemic lupus erythrematosus)[3] because of the rarity and lack of good understanding about it.

[citation needed] If rheumatoid arthritis is present and other symptoms occur that are not commonly found within RA itself, such as a palpable spleen, further testing should be done.

A palpable spleen is not always a clinical significance, therefore CT scan, MRI, or ultrasound can be administered in order to help diagnose the condition.

According to Poulin et al., dimensional guidelines for diagnosing splenomegaly are as follows:[18] RA in patients with Felty's syndrome is chronic (after 10–15 years), and presents with increased severity along with extra articular manifestations.

[19] There is no real treatment for Felty's syndrome, rather the best method in management of the disease is to control the underlying rheumatoid arthritis.

Immunosuppressive therapy for RA often improves granulocytopenia and splenomegaly; this finding reflects the fact that Felty's syndrome is an immune-mediated disease.